Magnetic circuits for stationary electrical induction apparatus



July 21, 1959 P. M. PRUNEAU 2,896,182

MAGNETIC CIRCUITS FOR STATIONARY ELECTRICAL INDUCTION APPARATUS Filed Aug. 21, 1956 Fig. 7

Fig 6 Pierre f Unite States MAGNETIC CIRCUITS FOR STATIONARY ELECTRICAL ENDUCTION APPARATUS The present invention relates to magnetic circuits as used for stationary electrical induction apparatus, and more particularly to magnetic circuits comprising laminated cores at least two of which are preferably of the cylindrical type with radially disposed magnetic sheets.

An object of the invention is to provide a novel yoke for magnetically uniting the cores in a stationary induction apparatus.

Another object of the invention is to provide a magnetic circuit comprising laminated cores two or more of which are preferably of at least partly cylindrical type and consist of radially disposed or involute magnetic sheets, and magnetic elements constituting the yoke for uniting magnetically the extremities of the cores. Each yoke element leading to a cylindrical core consists of thin magnetic sheets jointly assembled into a bundle which impinges radially against at least a portion of the periphery at an extremity of the cylindrical core. The main planes of the magnetic sheets of each bundle are arranged parallel to the axes of the cylindrical cores and the end zones of the sheets are so curved that their edges impinge against the edges of the core laminations. In order to converge towards the core the end zones of the yoke sheets are individually curved into a shape approximating that of an involute of the circle circumscribing the core.

Other features and advantages of the invention will appear from the following description of certain embodiments selected for illustration in the accompanying drawing, and the invention will be finally pointed out in the appended claims.

In the drawing,

Figure 1 is a side elevational view of a magnetic circuit incorporating the features of the present invention; a

Figure 2 is a top plan view of the same circuit showing the involute shape of magnetic sheets constituting the yokes;

Figures 3- and 4 are analogous views of another'embodiment of the invention; and

Figures 5, 6 and 7 are top plan views of three further embodiments of the invention.

Figuresl and 2 show a magnetic circuit comprising two main cores which may be used as a one phase transformer. Cores 1 and 2 consist, according to a known technique, of thin magnetic sheets or laminations which are arranged substantially in radial planes as is shown at 3 in Figure 2.

In all figures showing plan views of the magnetic circuits, the thicknesses of the magnetic sheets are represented for the sake of simplicity by a single line and, for the same reason, the magnetic sheets, although joined together are represented merely by a reduced number of separate lines.

The magnetic sheets of the cylindrical cores are held together by ring armatures 4 which are soldered to the bases of the cylindrical cores.

The magnetic circuit is completed by two yokes which magnetically connect the extremities of the cores. Each yoke consists of thin joined magnetic sheets 6 asatent 0 sembled in a bundle which impinges radially against the peripheral areas adjacent to the extremities of the cylindrical cores. The median zones of magnetic sheets 6 constituting the bundle are parallel with a plane passing through to the axes of the cores and each sheet is curved in the vicinity of the latter. In order to impinge against the periphery of an adjacent core, the end zones of the yoke sheets are curved substantially into the shape of an involute of the circle circumscribing the core.

As will be seen in Figure 2, the transverse edges of the curved end zones of the magnetic sheets 6 constituting a yoke 5 impinge jointly against the peripheral surfaces of cores 1, 2 and thus form extensions of the radial magnetic sheets of the cores. This results in the lines of induction having the same direction and the same density in every magnetic sheet constituting the yoke, thus permitting to use with an optimum efiiciency magnetic sheets of the so-called oriented grains.

The yokes thus constituted have the shape of a block having a width equal to the length of the circumference of the cores and a thickness which, in the case of a magnetic circuit with homogeneous cross-section, is equal to only one-fourth of the diameter of the core. Such yokes permit therefore to realise magnetic circuits of minimum bulk even though they present a substantial basis for placing the windings on the cores.

The magnetic sheets of the yoke may be evenly distributed on each side of the plane containing the axes of the cores to constitute two half yokes or symmetrical yoke elements 5a and 5b each encompassing one half of the periphery of the cores. Each yoke element consists of a bundle made up, for instance, by piling magnetic sheets of predetermined length over a thickness equal to half the circumference of the cylindrical cores and, by means of an appropriate shaping tool, the extremities of the bundle are then bent over cylindrical shaping members simulating the laminated cores 1 and 2 in such a way that each magnetic sheet takes the shape of an involute of a circle joined to a straight line portion parallel to the plane containing the axes of the cores and at the other extremity again the shape of an involute. The magnetic sheets kept in this position are afterwards united, for instance, by metallic armatures 7 and 8 soldered .to the edges of the magnetic sheets.

In addition or instead, the magnetic sheets may be glued together with a suitable resin at the time the magnetic sheets are assembled or by impregnation after assembly.

The yoke elements 5 and 5a constitute rigid blocks which are assembled with the cores 1 and 2 by means of tensioning members 9 resting on the one hand against the armatures 4 of the cores and on the other hand against the armatures 8 of the yoke elements.

Figures 3 and 4 represent a magnetic circuit which, too, may be used for a one phase transformer. This magnetic circuit comprises a main core 10 for the windings and two return cores 11 and 12. The main core is of cylindrical contour and consists of radial magnetic sheets disposed as sheets 3 of cores 1 and 2 described in Figures 1 and 2. The return cores 10 and 11 are semicylindrical with radial magnetic sheets having the same radius as that of the core 16. These semi-cylindrical cores are reinforced by suitable armatures 13a and 13b. The magnetic circuit is completed by yoke elements 14 consisting of bundles of magnetic sheets having end zones shaped as involutes of a circle and are thus analogous to yokes 5 described in connection with Figures 1 and 2, ex-

cept that the yokes 14 encompass only half of the periphery of semicylindrical cores 11 and 12.

The yoke elements 14 are kept in shape by suitable devices, for example, by armatures 15, soldered to the faces of yoke elements and may be assembled with the cores by means of tensioning elements (not shown) analogous to elements 9 shown in Figures 1 and 2.

Figure represents schematically a magnetic circuit with three main cores 16, 17 and 18 which may be used for a three phase transformer. These three cores are of cylindrical contour and consist of radial magnetic sheets; they are magnetically united by yokes 19 made up of magnetic sheets having involute end zones united with the extremities of the cores. The yokes 19 are assembled in the manner already described in connection with embodiments of Figures 1 to 4.

Figure 6 represents schematically the magnetic circuit of a monophased transformer with two cylindrical main cores 2t) and 21 consisting of radial magnetic sheets, and two return cores 22 and 23 of the parallelepipedic type. The cores are united magnetically yoke elements 24, 25 and 26 made up of magnetic sheets having end zones of involute shape. The yoke element 24 uniting the two main cores is identical with the yoke elements 14 of Figure 4. The yoke elements 25 and 26 are similar to approximately one half of yoke element 24 cut in a plane of symmetry perpendicular to Figure 6. It will be understood that the magnetic sheets of return cores 22 and 23 are piled up in order that the edges of said sheets meet the edges of the magnetic sheets of yoke elements 25 and 26. It will also be noted that the assembly of return core 22 and its associated yoke element 26 may be replaced by the equivalent assembly of a semicylindrical core 12 and its associated yoke element 14- shown in Figures 3 and 4. This magnetic circuit is equivalent to the magnetic circuit shown in Figures 1 and 2. It is somewhat longer but narrower.

Figure 7 represents schematically a magnetic circuit with three main cylindrical cores 27, 2S and 2& each consisting of radial magnetic sheets and two return cores 30, 31 of the semi-cylindrical type. The five cores are united by yoke elements 32 analogous to yokes I 3 of Figures 3 and 4.

This magnetic circuit may be used as a three phase transformer equivalent to the magnetic circuit of Figure 5. It will be noted, however, that this circuit is longer but narrower.

The invention, of course, is not limited to the exact details of embodiments hereinbefore described and shown in the drawing only by Way of example, but may be applied also to any magnetic assembly of a core or a portion of a cylindrical core with radial magnetic sheets and of a yoke consisting of a bundle of magnetic sheets impinging against the entire or a portion of the peripheral surface of the core.

Moreover, the yokes may be assembled in a single step by jointly bending the end zones of a number of narrow magnetic strips into the shape of an involute and then connecting the edges of the so formed yokes with the periphery of one or more cylindrical yokes.

What I claim is:

1. In a stationary induction apparatus, the combination of a plurality of at least partially cylindrical cores each consisting of a plurality of radially disposed laminations of magnetic material; at least one yoke element for magnetically uniting two selected ones of said cores, each of said yoke elements consisting of a plurality of magnetic sheets, each or" said sheets having a least one end zone shaped substantially as an involute of a circle circumscribing the adjacent one of said cores and in edge-toedge contact with one of said radial laminations of said core and means for maintaining said cores and said yoke elements as a rigid unit.

2. The combination according to claim 1, wherein said radial laminations of said cores and said sheets of said yokes are held together by an adhesive substance and said last named comprises metallic armatures for rigidly connectingsaid sheets of each of said yoke elements and said'laminations of said cores, respectively, said armatures Al being soldered to the exposed edges of said sheets and of said laminations, respectively.

3. In a stationary induction apparatus, the combination of a pair of cylindrical cores each consisting of a plurality of radially disposed laminations of magnetic material; at least one yoke element for magnetically uniting said cores, said yoke element consisting of a plurality of magnetic sheets, each of said sheets having a pair of end zones each adjacent to one of said cores, each of said end zones being shaped substantially as an involute of a circle circumscribing the adjacent one of said cores and in edge-to-edge contact with a lamination of said core; and means for maintaining said cores and said yoke element as a rigid assembly.

4. The combination according to claim 3, further comprising a pair of substantially parallelepipedic cores each adjacent to one of said cylindrical cores, each of said last mentioned cores consisting of a plurality of parallel laminations of magnetic material; at least one yoke element for magnetically uniting said last mentioned cores with the adjacent one of said cylindrical cores, each of said last mentioned yoke elements consisting of a pluralit-y of magnetic sheets, each of said sheets having a first end zone shaped substantially as an involute or" a circle circumscribing the adjacent one of said cylindrical cores and in edge-to-edge contact with a lamination of said cylindrical core, and a second end zone in a plane parallel with the plane of and connected with a lamination of one of said last mentioned cores.

5. In a stationary induction apparatus, the combination of three cylindrical cores each consisting of a plurality of radially disposed laminations of magnetic material; at least one yoke element for magnetically uniting two selected ones of said cores, each of said yoke elements consisting of a plurality of magnetic sheets, each of said sheets having a pair of end zones each shaped substantially as an involute of a circle circumscribing the adjacent one of said cores and in edge-to-edge contact with a lamination of said core; and means for maintaining said'cores and said yoke elements as a rigid assembly.

6. The combination according to claim 5, further comprising a pair of semicylindrical cores each consisting of a plurality of radially disposed laminations of magnetic material and each adjacent to one of said cylindrical cores; and at least one yoke element for magnetically uniting one of said semicylindrical cores with the adjacent one of said cylindrical cores, each of said last mentioned yoke elements consisting of a plurality of magnetic sheets, each of said sheets having a pair of end zones in the proximity of one of said semicylindrical cores and of the adjacent one of said cylindrical cores, respectively, said end zones being curved substantially as involutes of the circles circumscribing, respectively, one of said semicylindrical cores and the adjacent one of said cylindrical cores, said end zones of each of said sheets of said last mentioned yoke elements being in edge-to-edge contact with a lamination of one of said semicylindrical cores and of the adjacent one of said cylindrical cores, respectively.

7. In a stationary induction apparatus, the combination of two semicylindrical cores; a cylindrical core between said semi-cylindrical cores, each of said cores consisting of a plurality of radially disposed laminations of magnetic material; a pair of yoke elements for magnetically uniting each extremity of said cylindrical core with the respective extremities of each of said semi-cylindrical cores, each of said yoke elements consisting of a plurality of magnetic sheets, each of said sheets having a pair of end zones adjacent to said cylindrical core and to one of said semicylindrical cores, respectively, each of said end zones being curved substantially as an involute of a circle circumscribing the adjacent one of said cores and being in edge-to-edge contact with a lamination of the adjacent one of said cores; and means for maintaining said cores and said yoke elements as a rigid assembly.

8. In a stationary induction apparatus, the combination of a plurality of at least partially cylindrical cores having parallel axes in a comomn plane and each consisting of a plurality of radially disposed laminations of magnetic material; at least one yoke element for magnetically uniting two selected ones of said cores, each of said yoke elements consisting of a plurality of elongated magnetic strips, each of said strips having a median zone substantially parallel with the common plane of the axes of said cores and two end zones shaped substantially as involutes of circles circumscribing the cores magnetically united by said yoke, the transverse edegs of said end References Cited in the file of this patent UNITED STATES PATENTS 2,531,697 Meyerhans Nov. 28, 1950 2,550,500 Shell Apr. 24, 1951 2,579,308 Dole Dec. 18, 1951 

